https://bugs.gentoo.org/586828

Backported from:
https://git.gnome.org/browse/gimp/commit/?id=2e4685013123c584354bc38612527593a815c38b

--- gimp-2.9.2/app/core/gimpparamspecs-duplicate.c
+++ gimp-2.9.2/app/core/gimpparamspecs-duplicate.c
@@ -66,23 +66,11 @@
         }
       else
         {
-
           copy = g_param_spec_string (pspec->name,
                                       g_param_spec_get_nick (pspec),
                                       g_param_spec_get_blurb (pspec),
                                       spec->default_value,
                                       flags);
-
-          if (GEGL_IS_PARAM_SPEC_MULTILINE (pspec))
-            {
-              static GQuark multiline_quark = 0;
-
-              if (! multiline_quark)
-                multiline_quark = g_quark_from_static_string ("multiline");
-
-              g_param_spec_set_qdata (copy, multiline_quark,
-                                      GINT_TO_POINTER (TRUE));
-            }
         }
     }
   else if (G_IS_PARAM_SPEC_BOOLEAN (pspec))
--- gimp-2.9.2/app/widgets/gimppropgui.c
+++ gimp-2.9.2/app/widgets/gimppropgui.c
@@ -227,11 +227,6 @@
     }
   else if (G_IS_PARAM_SPEC_STRING (pspec))
     {
-      static GQuark multiline_quark = 0;
-
-      if (! multiline_quark)
-        multiline_quark = g_quark_from_static_string ("multiline");
-
       if (GIMP_IS_PARAM_SPEC_CONFIG_PATH (pspec))
         {
           widget =
@@ -239,7 +234,7 @@
                                                g_param_spec_get_nick (pspec),
                                                GTK_FILE_CHOOSER_ACTION_OPEN);
         }
-      else if (g_param_spec_get_qdata (pspec, multiline_quark))
+      else if (HAS_KEY (pspec, "multiline", "true"))
         {
           GtkTextBuffer *buffer;
           GtkWidget     *view;